Gas turbine engines, such as those used on jet aircrafts, generally comprise an air inlet, a fan, a single or multi-stage compressor, a combustion chamber aft (downstream) of the compressor, a single or multi-stage turbine, and an exhaust nozzle. Air entering the inlet flows through the compressor and into the combustion chamber where it is ignited. The hot combustion gases pass through the turbine and exit the exhaust nozzle, providing thrust.
The turbine is comprised of alternating rings of stationary vanes and rotating blades (collectively referred to as airfoils). The turbine blades are connected at their inner diameter ends to platforms having endwalls and extend radially outward therefrom. The platforms are connected to a rotor, which is connected to a shaft that rotates within the engine as the blades interact with the gas flow. Each platform typically comprises an axial retention slot or channel that receives the mating root portion of the blade.
The rings of radially extending stationary turbine vanes are located between the turbine blade rings. Each stationary turbine vane is mounted to a platform having an endwall.
During operation of the engine, the turbine airfoils, that is, the turbine blades and turbine vanes, are exposed to high heat from the combustion gases. In addition, the blades are subjected to high stresses from rotational forces. It is therefore a design challenge to develop materials for turbine blades and vanes that are more heat resistant to reduce airfoil cooling demands and are lighter to increase propulsive efficiencies in aircraft engines.
Typically, the airfoil members and their platforms are fabricated from high strength alloys. More recent airfoil member and its platform designs have attempted to incorporate a ceramic matrix composite (CMC) material, which is lightweight, heat resistant and strong. CMC material comprises a ceramic fabric that is infused with a ceramic matrix. The ceramic fabric is preformed to a desired shape and the matrix solidifies within the fabric to produce a part having the lightweight and heat resistant characteristics of the matrix and the strength characteristics of the fabric.
The rotating turbine blades drive the compressor. Like the turbine, the compressor is comprised of alternating rings of stationary vanes and rotating blades. Each ring is comprised of a plurality of radially extending airfoil members that are connected at their inner diameter ends to a platform having an endwall. Compressor airfoil member and/or its platform designs may incorporate an organic matrix composite (OMC) material.
CMC turbine airfoil member and platform assemblies and OMC compressor airfoil member and platform assemblies have the potential to revolutionize engine performance as they enable improved fuel efficiency, increased durability, higher thrust to weight ratio, and other benefits. To further enhance these benefits, the present disclosure provides an airfoil member and platform assembly in which the platform is made of a composite material and has an endwall that is contoured. Providing endwall contouring influences the flow of gases through the flow passages between the turbine blades and/or vanes, thereby reducing endwall losses due to horseshoe vortexing and improving aerodynamic performance.
Airfoils made from composite (CMC or OMC) materials offer good strength in its primary load path. Attaching a CMC or OMC platform onto the airfoil is difficult and especially challenging if the platform endwall is contoured.